Signal transducer and activator of transcription (STAT) activation and inactivation are controlled by protein tyrosine kinase (i.e., JAK) and protein tyrosine phosphatase (i.e., SHP-2) activities, respectively. C-terminal region phosphorylated STAT dimerize and translocate into nuclei where it binds to DNA for transcriptional activation. To achieve maximum transcriptional activity, STAT needs to interact with other nuclear factors. Evidence from our laboratory shows that both p300/CBP and HDAC family members are capable of forming complexes with STAT3 but exert opposite effects on STAT3-dependent transcription: while p300/CBP enhances STATS's activity in transcription, overexpression of the HDAC family member HDAC3 in 293T cells was highly effective in blocking STAT3-dependent transcription. Thus, p300/CBP and HDAC activities may play key roles in regulating STAT3 activity. Recently, STAT3 has been found to play an important role in regulating cell migration and tumor metastasis although the mechanism has yet to be determined. In this regard, STAT3 constitutive phosphorylation has been widely detected in both metastatic and non-metastatic cells. Thus, an additional post-translational modification event seems to be required for STAT3 to regulate gene transcription relevant to acquisition of the metastatic phenotype. The overarching hypothesis to be tested in this proposal is that STAT activity is under the control of acetylation and deacetylation mediated by HAT and HDAC, respectively. It is hypothesized further that constitutive STAT3 acetylation may play a central role in development of metastasis. To fully test these hypotheses, experiments will use our antibody array technology, specific gene-deficiency and/or down regulation, and mass-spectroscopy in order to: (1) explore HAT/HDAC as components of STAT3 signaling complex; (2) test STAT3 acetylation in STAT3 dimerization and resisting to inactivation/degradation; and (3) test the hypothesis that STAT3 acetylation plays a role in metastasis-related gene regulation and constitutive STAT3 acetylation is responsible for metastatic phenotype in vivo. These complimentary approaches will elucidate the role of uncontrolled STAT3 acetylation/deacetylation in causing cancer cell invasion and metasasis.